This information on sources for hydraulics would have been found in the Silver and Gold books. See examples below:
1948 Issue:
https://www.flickr.com/photos/advance-design_parts_co/16736434779/in/album-72157631872034068/
1954 Issue:
https://www.flickr.com/photos/advance-design_parts_co/16708704180/in/album-72157631872034068/
1954 Hydraulic page (several options):
https://www.flickr.com/photos/advance-design_parts_co/16894892712/in/album-72157631872034068/
These books contained sources for bodies, fire trucks, all specialized applications that a dealer could use to source customer options.